Electric lamp with electrolysis preventing apparatus

ABSTRACT

An electric lamp having a lamp envelope transmitting radiation which is sealed in a vacuum-tight manner at least one end by means of a pinch in which at least two current lead-through conductors are sealed. An electric voltage comprising a direct voltage component is present between these conductors during operation of the lamp. A metal scrreming element is placed in the pinch between the two current lead-through conductors. The screening element is connected to the current lead-through conductor which has as an average a negative potential relative to the other current lead-through conductor during operation so that the drawbacks of electrolysis phenomena in the pinch are eliminated.

United States Patent Spiessens et al.

[ 1 Sept. 16, 1975 Walter Jan Roza Adolf De Rop, both of Eindhoven,Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Apr. 24, 1974 Appl. No.: 463,738

[30] Foreign Application Priority Data A May 4, 1973 Netherlands 7306208[52] US. Cl. 313/318; 174/5059; 313/225; 313/229; 313/315; 315/60 [51]Int. Cl. H01J 5/50; H01J 61/36; H01J 61/54; HOIK H38 [58] Field ofSearch 313/332, 318, 315, 184, 313/219, 222, 197, 198, 315, 225, 229;174/5059, 50.64

[56] References Cited UNITED STATES PATENTS 1,985,028 12/1934 Gehrts174/5059 X 2,329,019 9/1943 Wagencr 174/5059 X 2,454,384 11/1948 Henry174/5059 X 2,569,848 10/1951 Eitel et a1. 174/5059 X 3,275,885 9/1966Pomfrett.... 313/197 X 3,668,456 6/1972 Anderson 313/318 PrimaryExaminerPalmer C. Demeo Attorney, Agent, or FirmFrank R. Trifari 5 7 1ABSTRACT An electric lamp having a lamp envelope transmitting radiationwhich is sealed in a vacuum-tight manner at least one end by means of apinch in which at least two current lead-through conductors are sealed.An electric voltage comprising a direct voltage component is presentbetween these conductors during operation of the lamp. A metal scrremingelement is placed in the pinch between the two current leadthroughconductors. The screening element is connected to the currentlead-through conductor which has as an average a negative potentialrelative to the other current 1ead-through conductor during operation sothat the drawbacks of electrolysis phenomena in the pinch areeliminated.

10 Claims, 3 Drawing Figures PATENTEU SEP 1 6 I975 sum 2 0 2 ELECTRICLAMP WITH ELECTROLYSIS PREVENTING APPARATUS The invention relates to anelectric lamp having a lamp envelope transmitting radiation and beingsealed in a vacuum-tight manner at at least one end by means of a pinchin which at least two current lead-through conductors are sealed.Particularly the invention relates to a dischargelamp provided with afirst and a second main electrode between which the dischargeisieffected during operation and an auxiliary electrode arianged in thevicinity of the first main electrode, the current lead-throughconductors for the first main electrode and for the auxiliary electrodebeing sealed in a pinch.

ln lamps of the above-mentioned kind a very disturbing electrolysisphenomenon may occur between the current lead-through conductors sealedin the pinch when during operation of the lamp a direct voltage ispresent as an average in time between these conductors. The material ofthe pinch consisting of glass or quartz glass then serves as theelectrolyte. It is assumed that the charge transport in thiselectrolysis phenome non is effected by alkali metal ions which occur inthe glass or quartz and which are displaced towards the negativeconductor. A result of the said electrolysis in the pinch of a lamp is adiscolouration and attack of the quartz or glass around the negativecurrent leadthrough conductor and possibly an attack of this conductoritself. The said attack may proceed after a large number of operatinghours to such an extent that the lamp drops out due to leakage, crackingof the pinch or even explosion. I

The above-mentioned drawbacks are particularly manifest in gas dischargelamps, for example, in highpressuremercury vapour discharge lamps whichin addition to mercury comprise one or more metal halides. These lampsgenerally have a hard glass or quartz glass discharge tube as a lampenvelope which is closed at both ends by a pinch. A main electrode isplaced within the discharge tube at each end which electrode is passedto the exterior by means of a current lead through conductor sealed inthe adjacent pinch. In order to obtain a vacuum-tight seal theselead-through conductors are at least partly formed as thin molybdenumfoils. An auxiliary electrode may be arranged in the vicinity of one ofthe main electrodes in such lamps, which auxiliary electrode is passedto the exterior by means' of a current lead-through conductor sealed inthe adjacent pinch and comprising a molybdenum foil and which outsidethe lamp is connected through a resistor to the other main electrode.This auxiliary electrode serves to facilitate the ignition of the lamp.During operation of these lamps which are fed by an alternating voltagean electric voltage is present between the auxiliary electrode and theadjacent rnain electrode, which voltage contains such a direct voltagecomponent that the auxiliary electrode has an average negative potentialrelative to the main electrode. The said direct voltage component is aresult of the fact that the main electrode more easily emits electronsthan the auxiliary electrode.

To prevent electrolysis in the pinch of a discharge lamp different stepsare known (see for example German Patent Application No. 2,052,060).These known steps include all relatively complicated circuits such asrectifiers and or temperature-dependent mechanical switches, such asbimetals which prevents the occurrence of the phenomenon ofelectrolysis. The known steps are, however, comparatively expensive andare found to be not always reliable in practice.

Electrolysis in the pinch of a lamp and the attendant difficulties arefound to occur also in electric incandescent lamps, for example, halogenlamps which are intended for direct voltage operation and in which thetwo current lead-through conductors are sealed in one pinch.

The invention provides electric lamps provided with simple means withwhich the drawback of the abovedescribed phenomenon of electrolysis canat least largely be obviated. The invention is based on the recognitionof the fact that it is not necessary to entirely prevent the occurrenceof electrolysis in the pinch of a lamp so as to avoid theabove-mentioned drawbacks of this electrolysis. v

An electric lamp according to the invention has alamp envelopetransmitting radiation and is sealed in a vacuum-tight manner at atleast one end by means of a pinch in which at least two currentlead-through conductors are sealed between which conductors an electricvoltage is present during operation of the lamp which voltage comprisesa direct voltage component and is characterized in that a metalscreening element is placed in the pinch between the two currentleadthrough conductors, the screening element not intersecting theinternal surface of the lamp envelope and being connected to the currentlead-through conductor which at an average has a negative potentialrelative to the other current lead-through conductor.

In a lamp according to the invention a metal screening element isincorporated in the pinch between the two current lead-throughconductors. The screening element is connected to the currentlead-through conductor which during operation, possibly as an average intime, has a negative potential relative to the other current leadthroughconductor. As a result the screening element will have the same negativepotential relative to the other current lead-through conductor. In thismanner the electrical field resulting from the direct voltage componentbetween the two current leadthrough conductors will be displaced for thegreater part to the region in the pinch between the positive currentlead-through conductor and the screening element. Consequently in a lampaccording to the invention the negative current lead-through conductoris screened in an effective manner from the electrical field resultingin electrolysis by the screening element located between this conductorand the positive current lead-through conductor. As a result theconsequences of electrolysis (discolouration and attack) on thisnegative current lead-through conductor are substantially completelyprevented. Only at a very late in stant of the lifetime of the lamp maythese electrolysis consequences occur (and then generally in anundisturbing manner) on the negative current lead-through conductor.

It is evident from the foregoing that in a lamp according to theinvention the electrolysis phenomenon is not prevented but is displacedto another part of the pinch. It has been surprisingly found thatelectrolysis between positive current lead-through conductor andnegative screening element in a lamp according to the invention can benoticed to a lesser extent on the screening element and does not lead toany harmful consequences for the lamp for a very long time. A conditionis, however, that the screening element does not intersect the internalsurface of the lamp envelope. In fact, it has been found that the lampquickly becomes defective when the screening element extends as far asthe space within the lamp envelope.

The invention is used very advantageously in electric lamps formed asgas discharge lamps because in such discharge lamps the electrolysisphenomenon may often occur to a very disturbing extent. Such a gasdischarge lamp according to the invention has a discharge space enclosedby the lamp envelope, which space comprises a gas filling and isprovided with a first and a second main electrode between which thedischarge takes place during operation and furthermore with an auxiliaryelectrode arranged in the vicinity of the first main electrode in whichthe current lead-through conductor for the first main electrode and thecurrent leadthrough conductor for the auxiliary electrode are sealed ina pinch, which conductors are substantially co-planar and comprise afoil mainly consisting of molybdenum and is characterized in that themetal screening element is placed in the pinch between the foils andsubstantially in the plane determined by the foils and that thescreening element has the same potential as the auxiliary electrodeduring operation.

Likewise as the known gas discharge lamps, the gas discharge lampsaccording to the invention have an auxiliary electrode which, asdescribed in the preamble, may be connected outside the lamp through aresistor to a main electrode and which serves to ignite the lamp easily.As a result of the difference in electron emission power betweenauxiliary electrode and the adjacent main electrode the auxiliaryelectrode has a negative potential during operation relative to the mainelectrode. The phenomena of electrolysis which conse quently might occuron the auxiliary electrode are prevented according to the invention by ametal screening element located between the current leadthroughconductors in the pinch. These conductors are substantiallyco-planar and the screening element is in the same plane. The screeningelement is connected to the current lead-through conductor for theauxiliary electrode in such a manner that this screening element assumesthe same potential as the auxiliary electrode. This constructionaccording to the invention provides a very satisfactory screening of thecurrent lead through conductor for the auxiliary electrode because thesaid conductor for the auxiliary electrode is substantially entirelyscreened by the screening element as viewed from the currentlead-through conductor for the main electrode.

It has been found that optimum results in gas discharge lamps accordingto the invention are obtained when the screening element extends as faras the vicinwithin the discharge space and in which the screeningelement extends in said elevation beyond the part of the currentlead-through conductor of the auxiliary electrode located in the pinch.A screening which is as complete as possible is obtained with thisconstruction while the risk of electrolysis along paths around the partof the screening element facing the discharge space is excluded as muchas possible.

It is possible to connect the screening element within the pinch to thecurrent lead-through conductor for the auxiliary electrode in order tobring the two components at the same potential. However, discharge lampsaccording to the invention are preferred in which the screening elementis passed to the exterior through the pinch and is connected outside thelamp to a conductor secured to the current lead-through conductor forthe auxiliary electrode. In fact, a reliable pinch seal can bemanufactured more easily in this manner.

The screening element may be, for example, a foil mainly consisting ofmolybdenum. However, a wire of high melting point metal is preferablyused, for example, tungsten, molybdenum or tantalum as a screeningelement. Such a wire-shaped screening element yields optimum results.

The invention is preferably used in high-pressure mercury vapourdischarge lamps which in addition to mercury also comprise a rare gas asa starter gas. In such lamps the phenomenon of electrolysis may be verydisturbing especially when the lamps are intended for the horizontaloperating condition where the auxiliary electrode is located below themain electrode.

Such high-pressure mercury vapour discharge lamps according to theinvention are especially preferred which in addition to mercury and arare gas comprise at least one metal halide. Notably when such ahalidecontaining lamps is provided with an alkali metal halide thephenomena of electrolysis may be very serious because alkali metal maypenetrate the material of the pinch from the discharge space and maycause an increase of a number of charge carriers and consequently anincrease of the electrolysis current.

The invention may likewise be used to great advantage in electricincandescent lamps, for example, in halogen lamps which are intended fordirect voltage operation and are provided with a filament body locatedwithin the lamp envelope which body can be connected to a direct voltagesource by means of two current lead-through conductors sealed in onepinch. The said current lead-through conductors are then substantiallyco-planar and comprise a foil mainly consistin g'of molybdenum.According to theinvention electrolysis in the pinch of such anincandescent lamp is prevented by a metal screening element placed inthe pinch between the foils and substantially in the plane determined bythe foils. The screening element is then connected to the negativeterminal of the voltage source during operation of the lamp.

The invention will now be described in greater detail with reference toa drawing in which FIG. 1 shows a metal halide-containing high-pressuremercury vapour discharge lamp according to the invention and in whichFIG. 2 is a cross-sectional of an embodiment of a pinch construction andscreening element for use in a lamp according to the invention.

FIG. 3 shows an incandescent lamp according to the invention.

In FIG. 1, l is the quartz glass discharge tube of a high-pressuremercury vapour discharge lamp according to the invention. The mainelectrodes 2 and 3 con sisting of tungsten spirals secured to tungstencurrent lead-through conductors 4 and 5 are present at the ends of thetube 1. These conductors 4 and 5 are passed in a vacuum-tight mannerthrough the pinches 6 and 7, respectively. The vacuum-tight seal isobtained by forming part of the conductors 4 and 5 as molybdenum foils 8and 9, respectively. An auxiliary electrode 10 consisting of a tungstenpin is placed in the vicinity of the main electrode 2. The auxiliaryelectrode 10 is passed in a vacuum-tight manner through the pinch 6 bymeans of a current lead-through conductor 1 1 comprising a molybdenumfoil 12. The tube 1 is suspended in a glass outer envelope 13 by meansof metal strips 14 and .15 which clamp about the pinches 6 and 7 and aresecured to the supporting terminals or current supply members 16 and 17,respectively. These supporting terminals 16 and 17 also serve as currentsupply members for the electrodes 2 and 3 and are passed in avacuumtight manner through the outer envelope 13 and are connected tothe contacts of the lamp cap 18. The auxiliary electrode 10 facing themain electrode 2 is connected outside the discharge tube 1 through aresistor 19 to the current supply conductor 17 for the main electrode 3.A screening element 20 is sealed in the pinch between the currentlead-through conductors 1 1, l2 and 4, 8 of auxiliary electrode 10 andmain electrode 2. This element 20 consists of a tungsten wire and islocated in the plane of the molybdenum foils 8 and 12. The wire 20extends in the pinch 6 up to a distance of approximately 2 mm from theinternal surface of the discharge tube 1 and is connected outside thelamp to the current supply conductor 21 for the auxiliary electrode 10.

The discharge tube 1 is provided with a quantity of mercury completelyevaporating during operation of the lamp and furthermore with theiodides of sodium, thallium and indium. Furthermore a quantity of raregas is introduced as an ignition gas into the tube 1. The distancebetween the electrodes 2 and 3 is approximately 40 mm. The lamp has apower of 400 W during operation.

Known lamps having a construction identical to that of the lamp shown inFIG. 1 but having no screening element 20 become defective in many casesafter an operating period of 1000 to 2000 hours as a result of attack ofthe quartz around the lead-through conductor 11, 12, particularly aroundthe part of the molybdenum foil 12. adjoining 11. In lamps according tothe invention having the construction shown in FIG. 1 there is nodiscolouration or only a very slight discolouration around thelead-through conductor 11, 12 after an operating period of severalthousand hours. In the lamps according to the invention a discolourationof the quartz around the screening element 20 is found to occur. Thisdiscolouration does not have any detrimental results.

FIG. 2 shows a preferred embodiment in a crosssection of a pinchconstruction and a screening element for a lamp according to theinvention. The reference numeral 120 denotes the quartz glass pinch bodywhich changes over to the quartz glass wall 121 of the lamp. The pinch120 has an elevation 22 projecting within the lamp. A screening element23 which extends into the elevation 22 is sealed in the pinch. Theelement 23 consisting of a tungsten wire extends in the pinch in thedirection of the inner surface 24 of the lamp wall up to beyond thoseparts of the portions 25 and 26 of the current lead-through conductors25, 27, 29 and 26, 28, 30 which are located within the pinch. Thescreening element 23 is connected outside the lamp to the currentlead-through conductor 25, 27, 29 which assumes a negative potentialduring operation of the lamp relative to the lead-through conductor 26,28, 30.

In FIG. 3 the reference numeral 30 denotes the wall of a halogenincandescent lamp according to the invention. The lamp is sealed by apinch 31 through which the current lead-through conductors 32, 34, 36and 33, 35, 37 are passed in a vacuum-tight manner. These conductorsprovide for the current supply of the filament body 38 consisting of atungsten spiral. The lamp is intended for direct voltage operation andthe conductor 33 is connected to the negative terminal and the conductor32 is connected to the positive terminal of a voltage source.Electrolysis phenomena on the negative current lead-through conductor33, 35, 37 particularly on the molybdenum foil 35 are prevented by thetungsten wire screening element 39 sealed in the pinch 31. The element39 is connected outside the pinch 31 to the negative currentlead-through conductor 33.

What is claimed is:

1. An electric lamp for use with an associated electric power supplywhich comprises: a radiation transmitting lamp envelope, means forsealing in a vacuum-tight manner at one end of said envelope, said meansincluding a pinch, at least two current lead-through conductorsextending through said pinch in sealed relation said lead-throughconductors having an electric voltage comprising a direct voltagecomponent being present between said conductors during operation of thelamp from the associated electric power supply, a metal screeningelement disposed in the pinch between the two current lead-throughconductors, said screening element not intersecting the internal surfaceof the lamp envelope and being connected to the current lead-throughconductor which at an average has a negative pontential relative to theother current leadthrough conductor during operation.

2. A lamp asclaimed in claim 1 wherein said lamp is a gas discharge lamphaving a gas-filled discharge space surrounded by said lamp envelope,said lamp including a first and a second main electrode between which adischarge is effected during operation, said lamp further including anauxiliary electrode arranged in the vicinity of said first mainelectrode, said lead-through conductors being connected to said firstelectrode and said auxiliary electrode respectively, said conductorsbeing disposed in substantially co-planar relationship and comprising afoil primarily consisting of molybdenum, said metal screening elementbeing disposed in the pinch between the foils and substantially in theplane determined by said foils, and means for maintaining said screeningelement at the same potential as said auxiliary electrode during lampoperation.

3. A gas discharge lamp as claimed in claim 2, wherein said screeningelement in said pinch extends up to at least a distance of 0.5 mm fromthe internal surface of the lamp envelope.

4. A gas discharge lamp as claimed in claim 2, wherein said pinch has anaxial portion projecting within the discharge space intermediate saidleadthrough conductors extending from said pinch into said lampenvelope, said screening element being disposed in said axial portion.

5. A gas discharge lamp as claimed in claim 2, wherein said screeningelement extends from said pinch and is connected outside said lamp to aconductor secured to said current lead-through conductor for saidauxiliary electrode.

6. A gas discharge lamp as claimed in claim 2, wherein said screeningelement is a wire of high melting point metal.

7. A lamp as claimed in claim 6 wherein said lamp is a high-pressuremercury vapour discharge lamp in which mercury and a rare gas as anignition gas are disposed in said discharge space.

8. A high-pressure mercury vapour discharge lamp as claimed in claim 7in which at least one metal halide is disposed in said discharge space.

9. A lamp as claimed in claim 8 wherein said halide is an alkali metalhalide.

10. A lamp as claimed in claim 1, said lamp being an incandescent lampfor use with an associated direct voltage supply, and having a filamentbody disposed within said lamp envelope, said current lead-throughconductors sealed in one pinch and being substantially co-planar andcomprising a foil primarily consisting of molybdenum, said metalscreening element being disposed in the pinch between the foils andsubstantially in the plane determined by the foils, and said screeningelement being connected to the negative terminal of the associateddirect voltage source during lamp operatlOl'l.

UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENTNO.I 3,906,275 DATED September 16, 1975 INVENTORQ) RAYMONDFRANCOIS SPIESSENS ET AL it is certified that error appears in theabove-identifiedpatent and that said Letters Patent are hereby correctedas shown below:

IN THE ABSTRACT line 7, "scrreming" should read -screening+ En'gncd andScaled this twenty-third 1y 0f March 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Parentsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CETTFTCATE 0FECTTQN PATENT NO. 3,906,275 DATED September 16, 1975 INV ENTOR(S)RAYMOND FRANCOIS SPIESSENS ET AL It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

IN THE ABSTRACT line 7, "scrreming should read -screening- Signed anSealed this twenty-third fly O March 1 976 {SEAL} Arrest:

C. MARSHALL DANN Commissioner ofParenrs and Trademarks RUTH C. MASONArresting Officer

1. An electric lamp for use with an associated electric power supplywhich comprises: A radiation transmitting lamp envelope, means forsealing in a vacuum-tight manner at one end of said envelope, said meansincluding a pinch, at least two current lead-through conductorsextending through said pinch in sealed relation said lead-throughconductors having an electric voltage comprising a direct voltagecomponent being present between said conductors during operation of thelamp from the associated electric power supply, a metal screeningelement disposed in the pinch between the two current lead-throughconductors, said screening element not intersecting the internal surfaceof the lamp envelope and being connected to the current lead-throughconductor which at an average has a negative pontential relative to theother current lead-through conductor during operation.
 2. A lamp asclaimed in claim 1 wherein said lamp is a gas discharge lamp having agas-filled discharge space surrounded by said lamp envelope, said lampincluding a first and a second main electrode between which a dischargeis effected during operation, said lamp further including an auxiliaryelectrode arranged in the vicinity of said first main electrode, saidlead-through conductors being connected to said first electrode and saidauxiliary electrode respectively, said conductors being disposed insubstantially co-planar relationship and comprising a foil primarilyconsisting of molybdenum, said metal screening element being disposed inthe pinch between the foils and substantially in the plane determined bysaid foils, and means for maintaining said screening element at the samepotential as said auxiliary electrode during lamp operation.
 3. A gasdischarge lamp as claimed in claim 2, wherein said screening element insaid pinch extends up to at least a distance of 0.5 mm from the internalsurface of the lamp envelope.
 4. A gas discharge lamp as claimed inclaim 2, wherein said pinch has an axial portion projecting within thedischarge space intermediate said lead-through conductors extending fromsaid pinch into said lamp envelope, said screening element beingdisposed in said axial portion.
 5. A gas discharge lamp as claimed inclaim 2, wherein said screening element extends from said pinch and isconnected outside said lamp to a conductor secured to said currentlead-through conductor for said auxiliary electrode.
 6. A gas dischargelamp as claimed in claim 2, wherein said screening element is a wire ofhigh melting point metal.
 7. A lamp as claimed in claim 6 wherein saidlamp is a high-pressure mercury vapour discharge lamp in which mercuryand a rare gas as an ignition gas are disposed in said discharge space.8. A high-pressure mercury vapour discharge lamp as claimed in claim 7in which at least one metal halide is disposed in said discharge space.9. A lamp as claimed in claim 8 wherein said halide is an alkali metalhalide.
 10. A lamp as claimed in claim 1, said lamp being anincandescent lamp for use with an associated direct voltage supply, andhaving a filament body disposed within said lamp envelope, said currentlead-through conductors sealed in one pinch and being substantiallyco-planar and comprising a foil primarily consisting of molybdenum, saidmetal screening element being disposed in the pinch between the foilsand substantially in the plane determined by the foils, and saidscreening element being connected to the negative terminal of theassociated direct voltage source during lamp operation.